Chalcogenide materials are widely used in read-write optical disks. These materials have at least two solid phases, generally amorphous and generally crystalline. Laser pulses are used in read-write optical disks to switch between phases and to read the optical properties of the material after the phase change.
Chalcogenide materials also can be caused to change phase by application of electrical current. This property has generated interest in using programmable resistive material to form nonvolatile memory circuits.
One direction of development has been toward using small quantities of programmable resistive material, particularly in small pores. Patents illustrating development toward small pores include: Ovshinsky, “Multibit Single Cell Memory Element Having Tapered Contact,” U.S. Pat. No. 5,687,112, issued Nov. 11, 1997; Zahorik et al., “Method of Making Chalogenide [sic] Memory Device,” U.S. Pat. No. 5,789,277, issued Aug. 4, 1998; Doan et al., “Controllable Ovonic Phase-Change Semiconductor Memory Device and Methods of Fabricating the Same,” U.S. Pat. No. 6,150,253, issued Nov. 21, 2000.
Accordingly, an opportunity arises to devise methods and structures that form memory cells with structures that use small quantities of programmable resistive material.